The present invention relates to method and apparatus for cleaning a boiler of a power generation plant, and in particular, to a boiler cleaning method and apparatus for removing oil components remaining in a boiler before a steady operation of the power generation plant.
In a boiler of a thermal power generation plant, or in an exhaust gas heat recovery boiler of a combined cycle power generation plant composed of gas turbine facilities and steam turbine facilities, there remains various kinds of oils such as grease and the like which have applied and adhered when manufacturing, assembling or repairing the boilers. If the boiler is operated in a state in which such oil components remain therein, these oils foam or adhere to the interior of a boiler tube, causing the problems such as carbonization, hardness scale, local superheat or the like. For this reason, after construction of the power generation plant, it is general that the interior of the boiler is subjected to a cleaning treatment before the operation thereof in order to remove remaining oils.
Referring now to FIG. 3, a conventional boiler cleaning method will be described below. FIG. 3 is a system diagram showing an arrangement in the vicinity of one of boiler drums of an exhaust gas heat recovery boiler in a combined cycle power generation plant.
A feed water pump 2 is connected to a boiler feed water pipe 1. During an operation of the boiler, water pressurized by the feed water pump 2 is supplied to a economizer 3, and thereafter, is fed to a boiler drum 5 via a feed water flow control valve 4. The water stored in the boiler drum 5 is heated and vaporized by a gas turbine exhaust gas flowing through an exhaust gas passage 7 in a vaporizer 6. The generated steam is superheated by a superheater 8, and then, is fed to a steam turbine. The boiler drum 5 is provided with a manhole 9.
In order to remove a residual oil remaining in the boiler drum 5 after the construction of the plant and before an operation thereof, in the known art, there is provided an alkali cleaning method in which a lid of the manhole 9 is opened, and alkali chemicals, e.g., various soda chemicals are injected through the manhole 9 into the boiler drum 5 as a cleaning liquid or deoiling cleaning method including a combined heating process, which is called as soda boiling method.
However, according to the conventional cleaning methods mentioned above, it takes much time and labor to open and close the manhole 9 of the boiler drum 5 generally having a large-scale and to perform attachment and detachment of a heat insulating material, and moreover, large-scale facilities are required for injecting chemicals. Further, many kinds of chemicals such as cleaning chemicals, neutralization chemicals and the like are used. For this reason, there have arisen problems of cost increasing and long cleaning time being required.
In recent years, the combined cycle power generation plant or the like requires large-scale facilities, and for this reason, in particular, there have arisen earnest demands that the cost required for construction or repairing is reduced, and a commercial operation can be started in the course of a short time. Accompanying with such demands, it is desired to reduce the cost relevant to boiler cleaning and to shorten a work time.